1. Field of the Invention
The present invention relates to an on board antenna.
2. Description of the Related Art
Conventionally, a planar antenna is known which comprises a radiation element provided on the same surface of, for example, an automotive window glass which is located on a passenger compartment side thereof and a substantially annular grounding conductor which surrounds the periphery of an outer edge portion of the radiation element at a position spaced away outwardly from the outer edge portion of the radiation element (for example, refer to Published Japanese Patent JP-A-2002-252520).
In addition, a planar antenna is known which comprises a spacer inclined in such a manner that a normal direction of the planar antenna is closer to verticality than a normal direction of an actual installation position (for example, the automotive-window glass) of the planar antenna in order to improve the receiving sensitivity relative to signals transmitted from, for example, an artificial earth satellite at a relatively high elevation angle (for example, refer to published Japanese patent JP-A-5-63424).
Incidentally, in installing the planer antenna according to the aforesaid conventional example on a vehicle, in the event that the planner antenna is installed on an automotive window glass such as a front windshield or rear window glass, for example, it is desired to prevent the antenna not only from interrupting the vision of occupants of the vehicle but also from deteriorating the external appearance of the vehicle.
However, in the event that the dimensions and layout of the planar antenna are regulated based on the external appearance of the vehicle, for example, there may be caused a risk that attaining desired transmitting and receiving properties is made difficult. In particular, in the event that the planar antenna is provided on the surface of an automotive window glass which is disposed so as to intersect a vertical direction, there is caused a problem that securing desired transmitting and receiving properties relative to vertical polarization is made difficult.